hammond organ

When I say “siren” what do you think of? Ambulances? Air raids? Sigh. I was afraid you were going to say that. We’ve got work to do.

You see, the siren played an important role in physics and mathematics about 150 years ago. Through the first half of the 1900s, this fine apparatus was trivialized, used for its pure noise-making abilities. During the World Wars, the siren became associated with air raids and bomb shelters: a far cry from its romantic origins. In this article, we’re going to take the siren back for the Muses. I want you to see the siren in a new light: as a fundamental scientific experiment, a musical instrument, and in the end, as a great DIY project — this is Hackaday after all.

Here’s a short film made by the Hammond Organ Company with the intent to educate and persuade potential consumers. Right away we are assured that Hammond organs are the cream of the crop for two simple reasons: the tone generator that gives them that unique Hammond sound, and the great care taken at every step of their construction.

Hammond organs have ninety-one individual electromagnetic tone wheel assemblies. Each of these generate a specific frequency based on the waviness of a spinning disk’s edge and the speed at which it is rotated in front of an electromagnet. By using the drawbars to stack up harmonics, an organist can build lush walls of sound.

No cost is spared in Hammond’s tireless pursuit of excellence. All transformers are wound in-house and then sealed in wax to make them impervious to moisture. Each tone wheel is cut to exacting tolerances, cross-checked, and verified by an audio specialist. The assembly and fine tuning of the tone generators is so carefully performed that Hammond alleges they’ll never need tuning again.

This level of attention isn’t limited to the guts of the instrument. No, the cabinetry department is just as meticulous. Only the highest-quality lumber is carefully dried, cut, sanded, and lacquered by hand, then rubbed to a high shine. Before it leaves the shop, every Hammond organ is subject to rigorous inspection and a performance test in a soundproofed room.

An Arduino was connected to the organ via a UNL2003 darlington array chip. This chip is driving some reed relays which make the organ connections to create the sine wave tones. With that hardware in place it’s a matter of formatting data to generate the target audio. [Forrest] wrote his own Arduino sketch which takes characters from the serial port (pushed over USB by the laptop), maps then to a stored 5×7 character font set, then drives the pins to produce the tones. As you can see in the clip after the break the resulting audio can be turned into quite readable text.

In the 60s 70s and early 80s, roadies would lug hundreds of pounds of musical equipment around to gigs. Although the 8×10 Ampeg bass cabinet wasn’t fun in the least, the absolute worst was the Hammond organ. These behemoths of tonewheel organs sounded great, but moving them was a pain. For better or worse, portable MIDI keyboards caught up with the sound quality of these old electromechanical monsters. Everything is still not right with keyboard players; a good set of organ foot pedals is still hard to come by. To solve this problem, [Jeremy] converted his old Hammond A-100 organ pedals to MIDI giving him all the feel and aesthetics of an ancient instrument without all the heft.

To transform the ancient A-100 bass pedals into a keyboard, [Jeremy] turned to the HighlyLiquid MIDI CPU. This small board provides a few dozen pins to wire up to switches and potentiometers. A new switch assembly was built for the bass pedals using a momentary push button switch under each key. These buttons are wired up to the MIDI CPU, and everything worked out wonderfully.

Although there’s no video of the newly portable Hammond organ in action (something off Zeppelin I, [Jeremy]…) there is a great Flickr photoset of the entire build. Awesome work, [Jeremy]